1. Field of the Invention
The present invention relates to a recording apparatus for applying a recording liquid (e.g., a toner) (to be referred to as an ink hereinafter) on a recording medium such as recording paper to record an image or the like.
2. Related Background Art
In recent years, along with the development of data processing systems, printers when used as peripheral devices of these data processing systems must satisfy requirements for high print quality and low cost. A serial printer as a recording apparatus which satisfies these requirements has been used in practice.
A recording apparatus of this type is generally used in a printer, a facsimile system, a copying machine, or the like. The recording apparatuses are classified into (1) a serial type apparatus for recording information or data one by one while a recording head is moved in a predetermined direction (to be referred to as a main scanning direction hereinafter), and (2) a line type apparatus having a recording head with recording elements corresponding to one recording line arranged in the main scanning direction, so that recording is performed line by line. In such a recording apparatus, every time line recording is completed, the recording medium is fed by a predetermined amount in a direction having a predetermined relationship with the main scanning direction, i.e., a direction perpendicular to the main scanning direction (to be referred to as a subscanning direction hereinafter). When one-page recording is completed, the recorded medium is discharged.
As a recording system for applying an ink to a recording medium, ink-jet, heat transfer, and wire dot systems are available. Among these systems, the ink-jet system has received a great deal of attention because it can perform high-speed recording with relatively high precision. The ink-jet system further includes (1) and (2) respectively systems utilizing heat energy and (1) and (2) respectively systems utilizing an air flow.
A page printer having an image memory having a capacity of at least one page is also commercially available. The page printer can form an image as a bit image in the image memory as in formation of an image on a display device and can record the formed image. A page description language (instructions) such as a post script for a page printer has been developed. When the page description language is used, its instruction (to be referred to as coded data hereinafter) is supplied to the page printer. The page printer generates an image as a bit image in the image memory on the basis of the coded data.
FIG. 10 is a block diagram showing an arrangement for outputting external coded data onto recording paper. This arrangement includes a central processing unit (CPU) 21 for controlling the overall operation of the recording apparatus and performing image development (to be described later), print drivers 23, 24, 25, and 26, a control switch 22, and print heads 27, 28, 29, and 30. Coded data consisting of instructions of the page description language are input to and temporarily stored in a buffer 31. The CPU 21 performs processing for developing the coded data stored in the buffer 31 into image data of a one-page bit image in an image memory 32 and sends output control data to the control switch 22. Upon reception of this data, the control switch 22 determines (selects) a specific one of print drivers and an image data output destination in accordance with the output image data. The started print driver receives the image data from the CPU 21.and outputs the data to the corresponding print head. The print heads eject yellow, magenta, cyan, and black inks, and a full-color image is recorded.
An actual image output operation will be described below.
FIG. 11 is a view showing a sample image developed in the image memory. This sample image has an image start point 1 and an image end point 2. The image developed on the bit map is scanned bit by bit in the main scanning direction indicated by arrow 3. When scanning reaches to the right end, the image is scanned by one dot in the subscanning direction indicated by arrow 4.
The above operation will be described with reference to a flow chart in FIG. 12. When an image output instruction in the form of the page description language is received from a host computer, the printer temporarily stores the instructions in the buffer 31 (step S1). A memory area for storing a developed image is reset (step S2), and image development using an interpreter is started (step S3). At the same time, this data is written in the image memory 32 (step S4), and data development is repeated (step S5), being performed four times, until development and write access of yellow, magenta, cyan, and black data have been completed. When the image development is completed (step S6), the image data in the image memory 32 are read out by the CPU 21 and are output to the respective print drivers 23 to 26, thereby completing a series of operations.
In order the maximize the printer performance as in the conventional case, when one-page image data is stored in the image memory 32 and a multi-color printer is arranged, a total of four pages must be stored in the memories. In addition, if an image has gradation, the memory capacity becomes a serious problem. Since RAMs are expensive, the total cost of the electronic products depends on the number of RAMs mounted on a circuit board. In addition, if a large number of RAMs are used, they occupy a large space within the printer. Therefore, a large number of RAMs cannot be used for low-end compact printers.
In recent years, along with the development of data processing systems, high-speed operations and high print quality, and low cost are required for printers serving as peripheral devices for these data processing systems. As a printing device which satisfies the above requirements, an electrophotographic printer using a laser has been commercially available.
A desk-top publishing system (DTP) which has recently been popular must cope with full-color requirements. Strong demand has arisen for multi-color printers compatible with full-color desk-top publishing systems. Under these circumstances, printers compatible with multi-color requirements have already been used in practical applications. Conventional electrophotographic printers use a laser, an LED, and a liquid crystal shutter as their exposure devices. An LED head and a liquid crystal shutter are becoming popular in these printers due to requirements for low cost and compactness.
FIG. 13 is a perspective view showing a structure near the exposure and developing devices in a conventional multi-color printer using a laser, LED, or liquid crystal shutter. Recording paper 351 is fed in a direction indicated by an arrow below paper 351 in FIG. 13. The printer includes a photosensitive belt 352, drive rollers 353 for driving the photosensitive belt 352, a transfer belt 354 for transferring an image formed on the photosensitive belt 352 to the recording paper 351, developing devices 355, 356, 357, and 358 for developing basic colors, and an LED or liquid crystal shutter type exposure device 359 commonly corresponding to the developing devices 355, 356, 357, and 358. The photosensitive and exposure processes are performed in the order yellow, magenta, cyan, and black.
The electrophotographic processes in the multi-color printer will be described with reference to FIG. 13.
An exposure image obtained by the exposure device 359 such as a laser, LED, or liquid crystal shutter is exposed on the photosensitive belt 352. A first electrostatic latent image formed by this exposure is developed by the developing device 358. Assume that the colors to be processed by the developing units 355, 356, 357, and 358 are black, cyan, magenta, and yellow, respectively. The first latent image is developed in yellow. When one-page development by the developing device 358 is completed, the image formed on the photosensitive belt 352 is transferred to the transfer belt 354. Any extra developing agent is removed from the photosensitive belt 352 by a cleaner (not shown), and the photosensitive belt 352 is charged again by a charger (not shown). The photosensitive belt 352 charged again upon one revolution is subjected to formation of a second latent image as an exposure operation for a magenta image in the next developing process. This process is substantially the same as that in development with yellow. The developed image is transferred to the transfer belt 354. Cyan and black images are sequentially formed on the transfer belt 354 by the same process as described above, the order named. When all the images are formed on the transfer belt 354, the recording paper 351 comes close to the transfer belt 354, and the multi-color image is recorded on the recording paper 351. The arrows in FIG. 13 are conveyance directions of the recording paper 351, the transfer belt 354, and the photosensitive belt 352. Such developing processes performed in units of colors as in a series of transfer operations are called a multi-path system. This system requires a simple mechanism. However, an output time per sheet is undesirably prolonged.
FIG. 14 shows exposure devices corresponding to the developing devices in the structure shown in FIG. 13. Components 351 to 358 in FIG. 14 are the same as those in FIG. 13, and a detailed description thereof will be omitted. Exposure devices 360 to 363 correspond to the developing devices 355 to 358, respectively. The photosensitive belt 352 is charged by a charger (not shown), and exposure is started from the front exposure device. In the case of FIG. 13, the developing devices are arranged in an order of yellow, magenta, cyan, and black from the front side of the rotational direction. Therefore, the developing agents are applied to the transfer belt 354 in the above order.
FIG. 15 is a block diagram showing an operation wherein external input image data are output onto recording paper. This arrangement includes a central processing unit (CPU) 371 for controlling a recording apparatus body and input data, exposure drivers 373, 374, 375, and 376, a control switch 372 for controlling the above drivers, and exposure devices 377, 378, 379, and 380. The CPU 371 receives the input data and sends output control data to the control switch 372. When the control switch 372 receives the output control data from the CPU 371, the control switch 372 determines a specific one of the exposure drivers in accordance with image data to be output, thereby determining an image data output destination. The started one of the exposure drivers 373 to 376 receives the image data from the CPU 371 and outputs data to a corresponding one of the exposure devices 377 to 380.
FIG. 16 is a view showing a sample developed in an image memory. Positions indicated by arrows 1 and 2 are image start and end points, respectively. The image developed in the bit map is scanned dot by dot in the main scanning direction indicated by an arrow 3. When scanning reaches to the right end dot, the image is scanned by one dot in the subscanning direction indicated by an arrow 4.
The above operation will be described with reference to a flow chart in FIG. 12. When an image output instruction in the form of a page description language is sent from a host computer (not shown) to the printer, the printer causes a language storage buffer (not shown) to temporarily store this description language (step S1), resets a memory area in which a developed image is written (step S2), and starts image development by an interpreter (step S3). Data is written in the image memory simultaneously with this development (step S4). Data development is repeated until the end of the data (step S5). In a multi-color printer, data development and write access are repeated four times, i.e., in the order yellow, magenta, cyan, and black. When image development is completely performed, the written image data is output (step S6), thereby completing the series of operations.
In order to maximize the printer performance as in the conventional case, when one-page image data is stored in the image memory and a multi-color printer is arranged, a total of four pages must be stored in the memories Since RAMs (random access memory) are expensive, the total cost of the electronic products depends on the number of RAMs mounted on a circuit board. In addition, if a large number of RAMs are used, they occupy a large space within the printer. Therefore, a large number of RAMs cannot be used for low-end compact printers.